The present invention relates to a tripod type constant velocity universal joint for use in, but not exclusively, a front-wheel drive automobile.
An example of the tripod type constant velocity universal joint for transmission of torque from a driveshaft of a front-wheel drive automobile to a front wheel at a constant velocity is shown in FIGS. 9A to 9C. The joint shown comprises a cup-shaped outer joint member 1 having three axially extending part-cylindrical guide grooves 2 equally spaced in its inner periphery and an inner joint member, or tripod member, 4 inserted in the outer joint member and having three trunnions 5 projecting radially outwardly of the inner joint member 4. A roller 7 is rotatably carried by each trunnion 5 through a series of rolling elements 6 and is received in the corresponding guide groove 2 of the outer joint member 1. The guide groove 2 forms a pair of circumferentially opposing track surfaces 3 parallel to a rotational axis of the outer joint member. An outer periphery of the roller 7 in section is convex and complementary to the track surface 3. Each roller 7 is movable within the corresponding guide groove 2 while rolling along the track surfaces 3 and rotating about the trunnion 5.
When the joint transmits torque with the outer and inner joint members 1 and 4 at a working angle of .theta. as shown in FIG. 9B, the roller 7 tilts relative to the track surface 3 as shown in FIG. 9C. In this case, the roller 7 is about to roll in the direction indicated by arrow t in FIG. 9B, but since the track surface 3 extends parallel to the axis of the outer joint member, the roller 7 actually has to slide while being restrained by the track surface 3. This leads to scuffing of the roller 7 as it moves along the track surface 3, producing not only frictional heat but also a greater frictional resistance and accordingly an induced thrust in the axial direction. Such induced thrust causes vibration and noise of the car body, and should preferably be reduced as much as possible.
In the tripod type constant velocity universal joint various attempts have been made to reduce the induced thrust, and some examples are shown in FIG. 10 to FIG. 12.
FIG. 10 shows a dual-roller arrangement in which an inner roller 11 is rotatably fitted externally on a cylindrical outer periphery of a trunnion 5a of an inner joint member 4a through a plurality of rolling elements 6a, and a cylindrical inner periphery of an outer roller 12 is rotatably fitted externally on an outer periphery of the inner roller 11. The outer periphery of the inner roller 11 is a truly part-spherical surface having its center on the axis of the trunnion 5a, and the inner periphery of the outer roller 12 slides on this truly part-spherical surface, so that the outer roller 12 is tiltable relative to the trunnion 5a. The outer roller 12 is received in a guide groove 2a of an outer joint member la, and is movable axially of the outer joint member while rolling along track surfaces 3a of the guide groove 2a. When the joint transmits torque with the outer and inner joint members la and 4a at a working angle, the trunnion 5a together with the inner roller 11 tilts relative to the outer roller 12, while the outer roller 12 is guided by the track surfaces 3a of the outer joint member 1a so as to keep a position parallel to the axis of the outer joint member 1a, correctly rolling along the track surfaces 3a. Therefore, the frictional resistance and induced thrust are reduced to a certain extent.
In the joint shown in FIG. 11, an outer periphery of a trunnion 5b of an inner joint member 4b is substantially part-spherical, and an annular roller 13 is rotatably and tiltably fitted externally on this part-spherical outer periphery through a plurality of rolling elements 6b. When this joint transmits torque with the outer and inner joint members 1b and 4b at a working angle, the trunnion 5b tilts relative to the roller 13, while the roller 13 is guided by track surfaces 3b at opposite sides of a guide groove 2b of the outer joint member 1b so as to keep a position parallel to the axis of the outer joint member 1b, correctly rolling along the track surfaces 3b. In this case, too, the frictional resistance and induced thrust are reduced to a certain extent.
The basic structure of the joint shown in FIG. 12 is the same as that of the joint shown in FIG. 11, that is, an outer periphery of a trunnion 5c of an inner joint member 4c is truly part-spherical, and an annular roller 14 is rotatably and tiltably fitted externally on this truly part-spherical periphery through a plurality of rolling elements 6c. In this joint, too, when transmitting torque with the outer and inner joint members 1c and 4c at a working angle, the trunnion 5c tilts relative to the roller 14, while the roller 14 is guided by track surfaces 3c at opposite sides of a guide groove 2c of the outer joint member 1c so as to keep a position parallel to the axis of the outer member 1c, correctly rolling along the track surfaces 3c, and therefore the frictional resistance induced thrust are reduced to a certain extent.
In the known arrangements as mentioned above, however, as the joint rotates for transmission of torque between the outer and inner joint members and the roller of the inner joint member moves along the corresponding guide groove of the outer joint member, the roller is pressed against either one of the track surfaces at opposite sides of the guide groove, which can cause the roller to tilt as viewed in a cross section perpendicur to the axis of the outer joint member between the track surfaces. This will now be described in relation to the outer roller 12 of the joint shown in FIG. 10. As shown in FIG. 13 which is an enlarged view in part of FIG. 10, when torque is transmitted as the roller 12 is relatively pressed against the left track surface 3L, there is a slight clearance between the roller 12 and the right track surface 3R. Accordingly, the non-load side 12n diametrically opposite to the loaded side 12m of the roller 12 can be raised or lowered, with the fulcrum at the outer peripheral central part P.
When the roller 12 tilts radially outwardly of the outer joint member 1a as indicated by solid line in FIG. 13, the roller 12 comes in contact with a shoulder 8a formed in the guide groove 2a at its end surface on the non-loaded side 12n, producing a frictional resistance. The shoulders 8a extend parallel to the axis of the outer joint member along the right and left track surfaces 3R and 3L in order to prevent the roller 12 from tilting within the guide groove in the plane including the axis of the outer joint member. Similar shoulders are provided as required in the joints of FIG. 11 and FIG. 12. On the contrary, when the roller 12 tilts radially inwardly of the outer joint member 1a as indicated by chain line in FIG. 13, the outer periphery of the roller on the non-load side 12n comes in contact with the right track surface 3R as at S, where a frictional resistance is produced.
The frictional resistance caused by the tilting of the roller 12 is considered to be one of the causes for worsening the induced thrust or slide resistance in the tripod type constant velocity universal joint, and should desirably be reduced as much as possible. However, its reduction has heretofore been limited to such an extent that accuracy in manufacturing and assembling parts permits. Similar problems can also arise in the roller 13 in the joint of FIG. 11 or the roller 14 in the joint of FIG. 12.
It is hence a primary object of the invention to provide a tripod type constant velocity universal joint with the induced thrust and slide resistance substantially reduced by suppressing tilting movements of the roller of the inner joint member in the guide groove of the outer joint member.